This invention broadly relates to a composition and process for the electrodeposition of copper, and more particularly, to a composition and method for the electrodeposition of copper from aqueous acidic copper plating baths, especially from copper sulfate and fluoroborate baths. More specifically, the invention relates to the use of a novel brightening and leveling system comprising a mixture of selected compounds to produce a bright, ductile, level copper deposits with good recess brightness on metal substrates, particularly printed wiring boards, over a wide range of bath concentrations and operating current densities.
A variety of compositions and methods have heretofore been used or proposed for use incorporating various additive agents for electrodepositing bright, level, ductile copper deposits from aqueous acidic copper electroplating baths. Typical of such prior art processes and compositions are those described in U.S. Pat. Nos. 3,267,010; 3,328,273; 3,770,598 and 4,110,176 and pending U.S. patent application Ser. No. 122,204, filed Feb. 19, 1980, now U.S. Pat. No. 4,272,335, which are assigned to the same assignee as the present invention. According to the teachings of U.S. Pat. No. 3,267,010, it has been found that bright, level and ductile deposits of copper can be produced from an aqueous acidic copper electroplating bath incorporating therein a bath-soluble polymer of 1,3-dioxolane, preferably in conjunction with supplemental brightening agents including organic sulfide compounds; U.S. Pat. No. 3,328,273 teaches the use of a bath-soluble polyether compound containing at least 6 carbon atoms as a brightening agent, preferably in conjunction with aliphatic polysulfide compounds; U.S. Pat. No. 3,770,598 teaches the use of a bath-soluble reaction product of polyethyleneimine and an alkylating agent to produce a quaternary nitrogen as a brightener, preferably in conjunction with aliphatic polysulfides, organic sulfides and/or polyether compounds; U.S. Pat. No. 4,110,176 teaches the use of a bath-soluble poly (alkanol quaternary ammonium salt) as a brightening agent such as produced from the reaction of a polyalkylenimine with an alkylene oxide; while pending U.S. patent application Ser. No. 122,204 teaches the use of a substituted phthalocyanine radical as a brightening agent in acid copper plating baths, preferably in conjunction with secondary supplemental brightening agents.
While the compositions and methods described in the aforementioned United States patents provide for excellent bright, ductile, and level copper deposits, some difficulty has been encountered in achieving proper leveling over imperfections in the holes of printed wiring boards comprising recessed low current density areas. The novel brightening and leveling system of the present invention is particularly applicable for copper plating of electronic circuitry printed wiring boards in achieving bright, level, ductile deposits which have the unexpected special ability to provide level deposits over imperfections in the apertures of such printed circuitry boards.